Turbochargers used with engines, such as internal combustion engines, generally provide compressed air to an engine intake. The compressed air may allow additional fuel to be combusted within the engine cylinders, and, therefore the engine's horsepower may be increased while keeping the engine substantially the same size. As such, incorporating turbochargers into internal combustion engines may allow for smaller engines to be used without sacrificing the engine horsepower. Furthermore, using a turbocharger may help improve fuel economy, reduce engine emissions, and increase overall engine efficiency by providing more complete combustion of the fuel injected into the engine cylinders.
In general, a turbocharger typically includes a turbine housing connected to the engine's exhaust manifold, a compressor housing connected to the engine's intake manifold and a rotatable shaft enclosed in a center bearing housing coupling the turbine and compressor housings together. The turbine housing may enclose a turbine wheel which is rotatably driven by an inflow of engine exhaust delivered through the exhaust manifold. Moreover, the turbine wheel is mounted on one end of the rotatable shaft while a compressor wheel is mounted on the opposite end of the shaft. As a result, the rotation of the turbine wheel simultaneously causes a rotation of the compressor wheel. As the compressor wheel rotates, air is drawn into the compressor through an inlet which directs the air towards the rotating compressor wheel. As the air interacts with the compressor wheel it is compressed such that there is an increase of the air mass flow rate, airflow density and/or air pressure delivered through the engine's air intake to the engine cylinders.
While rotational speed of the turbines and compressors can vary based on the size of both the turbine and compressor wheels used, in general, the turbine wheels and compressor wheels rotate at very fast rates. For example, the turbine wheel and shaft assemblies may rotate at speeds up to 300,000 RPM causing the compressor wheel to rotate at similar speed. Furthermore, during certain compressor operating conditions, such as but not limited to periods of maximum flow capacity, the interaction between the incoming air and rotating compressor wheel produces an audible noise source which may be unacceptable to vehicle passengers and other individuals in the vicinity of the operating vehicle. As a result, noise reducing strategies need to be incorporated into turbochargers to help combat the unacceptable noise levels while maintaining or increasing the operational turbocharger efficiency.
In some designs, turbochargers may incorporate multiple airflow pathways that can improve turbocharger performance across a broad range of airflow conditions. Furthermore, the airflow pathways may be formed to minimize turbulence of the airflow as it moves through the pathway. As a result, the less turbulent airflow may help increase overall turbocharger efficiency by improving the interaction between the incoming airflow and the rotating compressor wheel. Furthermore, shaping or spinning the airflow in a particular direction may help reduce the noise generated by the turbocharger. For example, spinning airflow in the opposite direction as the compressor wheel rotation may help increase the attachment time between the airflow and the compressor blade, and this increased attachment time may help reduce some of the noise which is generated by the turbocharger.
U.S. Pat. No. 7,475,539 (hereinafter the ‘539 patent’) discloses a compressor housing incorporating an annular bypass port. The compressor housing further includes radial ribs which extend along a helical path through the annular bypass port. While such helical pathway may help in directing certain portions of the airflow they do not help minimize the turbulence or minimize noise. Therefore a turbocharger compressor housing, which includes features to minimize airflow turbulence and noise is needed.